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Патент USA US3045718

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July 24, 1962
Filed Jan. 12, 1959
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July 24, 1962
Filed Jan. 12, 1959
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July 24, 1962
Filed Jan. 12, 1959
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United States Patent 0 ” IC€
Patented July 24, 1962
George E. Ziegler, Evanston, Ill., assignor, by mesne as
signments, to Concrete Thermal Casings, Inc., Seattle,
Wash., a corporation of Washington
Filed Jan. 12, 1959, Ser. No. 786,169
5 Claims. (Cl. 138-106)
in insulation. Thus a modest amount of residual moisture
can cause a signi?cant fuel dollar loss over a period of
It is therefore a ?rst and principal object of my inven
tion to protect heat distribution systems from water de
terioration by continuously removing water and water
vapor from the system at a rate approaching or even ex
ceeding the average rate at which water enters the system.
A further and principal object of my invention is to
The present invention relates to improved heat distribu 10 make it possible to operate heat distribution systems with
improved thermal performance without the use of pro
tion systems and more particularly to systems having in
tective casings surrounding the insulation.
creased resistance to deterioration by water and ‘a method
A further object ‘of my invention is to make possible
for producing same.
the economical operation of heat distribution systems with
Heat distribution systems usually consist of one or
semi-permeable casings surrounding the insulation.
more heated ?uid-carrying pipes surrounded by suitable
Another object is to remove water from the thermal
thermal insulation. My present invention is applicable to
insulation by direct drainage.
underground systems in which the pipe and insulation
Another objective is to remove water vapor from the
are buried in the ground, and to overhead systems in which
the pipe and insulation are supported in ‘air by suitable ' thermal insulation by evaporation.
Another object is to minimize the entry of water by in
structures either above grade or in tunnels. vIn both classes 20
?ltration from ?ooded ground or from rain in the case
of systems it has been customary to protect the insulation
of overhead systems.
from-in?ltration of water from the ground and from rain
A further objective is to provide a path of maximum
by surrounding the insulation with a casing which may be
resistance to the ?ow of water through the insulation.
metallic or nonmetallic. The heated ?uids most com
monly encountered are hot water, steam, high temperature 25 A still further objective is to provide pipe support when
such support is needed ‘as well as providing for such re
(high pressure) hot water and heated oils.
quirements as thermal insulation, the inhibiting of cor
In the past, efforts have been made to improve the
rosi-on of the pipes and associated metal supports, and
water migration resistance of the thermal insulation and
in the case of underground systems, to protect the pipes
to devise watertight'casings; nevertheless, a recent author
itative engineering study reports that in heat distribution 30 from mechanical forces transmitted through the earth.
Many and further objects of the invention as well as
systems now in operation, water is the major adverse fac
advantages and features thereof will be ‘apparent from
tor encountered and that all systems eventually become
the discussion of the invention which follows, and it will
wet.- Water enters the distribution systems from internal
be understood moreover, in said discussion which more
pipe breaks, from in?ltration from the ground, from ?ood~
speci?cally describes the invention, that the same is not
ed manholes, or from rain leaking through the casings,
depending on the class of the system.
My invention is applicable to ?eld-fabricated poured
in-place heat distribution systems. These include systems
of the Golf type, Patent Number 2,355,966, in which the.
pipes are supported by the insulating concrete, as well
as systems in which the pipes are supported on conven
tional guides, rollers or rockers, and the insulation con
to be taken in a limiting sense but merely as illustrative
of the invention the metes and bounds of what is to be
considered patentable therein being de?ned by the ap
pended claims.
A fuller understanding of the invention may be had by
referring to the following description taken in conjunction
with the accompanying drawings in which:
sisting of insulating concrete or bituminous material which
is fused or solidi?ed by heat serve only thermal purposes.
FIGURE 1 shows a longitudinal cross section of a
and installed in tunnels or above grade.
FIGURE 3 is a cross sectional view ‘of a heat distribu
short length of heat distribution system with evaporation
My invention is also applicable to heat distribution‘ 45 and drainage channel.
FIGURE 2 is a cross sectional view taken along the line
systems utilizing preformed or sectional insulation placed
A--A of FIGURE 1.
on pipes supported on conventional supports and guides
tion system with multiple evaporation channels.
Heat distribution systems require protection from tWo
types of di?iculty with water. The ?rst of these dii?cul 50 FIGURE 4 illustrates cross sections of four shapes for
ties is the occasional ?ooding of the insulation from major
evaporative channels.
breaks in the ?uid distribution pipes, from unusual ground
water ?ooding, from back pressure of water through the
zation of water.
insulation caused by ?ooded manholes or from severe
In this ?ooded condition the system can not be satisfac
torily operated because of attendant violet boiling action
within this insulation. This boiling action is disastrous
to the physical structure of the insulation as well as proa
hibitively expensive as far as heat loss is concerned. The
boiling action can also result in pipe corrosion.
FIGURE 5 shows a concentric channel for the vapori
FIGURE 6 shows a modi?ed concentric channel for
theivv-aporizdation of water.
FIGURE. 7 is a graph of insulation temperature as a
function of distance from the surface of a 350° F. heated
FIGURE 8 is a graph ofinsulation temperature ‘as a
function of distance from the surface of a 750° F. heated
The second di?iculty is much less obvious than the ?ood
FIGURE 9 is 1a graph of thermal loss of heat distribu
ed state with its boiling action. However, it is equally
tion system.
FIGURE 10 is apparatus for measuring water migra~
serious especially since the condition is apt to prevail dur~~
ing the entire operating ‘life of the heat distribution sys 65 tion resistance of insulation.
tem. This second difficulty is the more or less permanent
FIGURE 11 is a cross section of sectional preformed
reduction in insulation performance caused by the presence
insulation equipped with evaporative' channel.
‘ FIGURE 12 shows a multiple pipe system with mul
of moisture in the insulation. It is well known that the
insulating values of all materials diminish rapidly with,
tiple ev-aporative channels.
‘increasing moisture content. A one percent increase in 70 FIGURE 13 shows water migration paths and isother—
mal curve in a heat distribution system with casing and
moisture content will ‘result in from two to four percent
evaporative channel.
increase in thermal conductivity, with a corresponding loss
general the possible difference in level of the channel 22
tion paths for a multiple pipe system.
inside the insulation is small compared to the normal
FIGURE 15 shows water migration paths for water
variations in elevation introduced along a run of pipe in
from break in pipe.
.. ,
the average distribution system. The variation in eleva
The general aspects of the operation of my invention 5 tion is needed to provide for internal drainage of the heat
can be most easily understood by considering it in rela
ed ?uid distribution pipes or to take care of variations
tion to past practices. In the past, attempts have been
in terrain.
made to minimize the entry of water into the heat distri
Even after ?ood water has been drained off through
bution system through the use of an external casing to
cocks 21, the moisture content of the insulation remains
keep out the water, and by waterproo?ng admixes added
high enough to cause excessively high heat losses. In
to the insulation to reduce the rate of migration of any
my invention as illustrated by FIGURE 1, this moisture
water which might accidentally enter through the casings
is evaporated from the insulation into channel 22 and re
or come from breaks in the heat distribution pipes. Since
moved from the channel by air which circulates either
the casings surround the insulation and are essentially
as natural draft resulting from a thermal syphon action
FIGURE 14 shows isothermal curve and water migra
continuous and relatively impervious to water vapor, no 15 in the vertical vents 27 and 28 or by induced draft from
appreciable evaporation of water can take place. In fact,
water accumulated in the insulation because the quantity
of water as liquid that was drawn into the insulation by
temperature changes through accidental openings in the
a fan 26. The intake pipe 27 and the exhaust pipe 28
are protected from the entry of rain by any conventional
type hood of which the inverted U 29 is one example.
The channel 22 may communicate at its ends to free or
casing in a given length of time is larger than the amount 20 open air or it can open into ventilated manholes or base
ments. For long runs of pipe a multiplicity of outlets
ing in an equal time. In sharp contrast to this situation,
and inlets can be used as a means of increasing the rate
my invention makes it possible to shift at will the balance
of evaporation. These are design variations which all
of Water that can leave as vapor through the same open
between water intake and water vapor outgo so that the
come within the scope of my invention.
system on the average over an extended period of time
In general the rate of evaporation of water from the
insulation into the channel 22 is dependent on the aver
age temperature and the percentage of moisture content
will dry out instead of accumulating water.
In addition to providing for the evaporation of water,
my invention provides for the drainage of excess or ?ood
of the insulation surrounding the channel.
water from the insulation.
FIGURES 7 and 8 show typical temperature gradients
In the past it has not been possible to use insulation 30 through insulations containing moisture for a direction
without casings in systems exposed to the weather above
B—B of FIGURE 2, with distances measured out from
grade or buried underground systems because the mois
the surface of the insulation for a section of insulation
ture content of the insulation increased too rapidly to
as shown in FIGURE 2 for two different pipe tempera
constitute a satisfactory system. My invention causes the
tures and two different insulation thicknesses.
removal of water vapor to be rapid enough so that the 35
The moisture level in the insulation depends on a num
moisture content of the insulation will not build up to
ber of factors. An important factor is the resistance of
an objectionable level, thus making it possible to operate
the insulation to the ?ow of water. The resistance of
systems constructed Without casings.
?ow or migration is different vfrom capillary absorption
This invention represents an improvement over the pipe
into dry material which is often erroneously measured
insulation systems broadly disclosed and claimed in the 40 to give an indication of permeability of water soaked ma
applications of Lincoln L. Loper, Jr., Serial Nos. 689,584
terials. With increasing resistance, the rate at which
now abandoned and 9,03 6.
water is added to any section of the insulation becomes
My invention introduces the idea of controlled rate of
smaller and it is easier to overbalance the water intake
evaporation by placing an evaporation channel at a loca
with the evaporation or vapor outgo.
tion in the body of the insulation where the temperature
Water migration resistance can be measured with the
'Will be appropriate to produce a rate of evaporation
apparatus shown in cross section in FIGURE 10 in which
greater than the rate at which water can enter the insula
a six inch diameter, twelve inch high cylinder 30, of the
tion either from small leaks in the heated ?uid pipe or
insulation provided with a cylindrical cavity two inches
from in?ltration from outside the system or both together.
in diameter and eight inches deep, is immersed ten
Details of this will be presented through the speci?c 50 inches in water 32 contained in a closed vessel 33. The
examples of my invention.
resistance can be measured in terms of water ?owing into
It should be pointed out that a small thermal loss is
the cavity 31 and then expressed as volume of water per
caused by- the evaporation of the water from the insulation
unit of time per square inch of cross section of insula
and from the warming of the air which circulates to re
move the water vapor. This loss however is negligible
In speci?c examples of my invention to be discussed
compared to the relatively large thermal conductivity loss
later, insulation will be characterized as being of low re
that can take place from the heated pipe to the surround
sistance if an appreciable amount of water accumulates
ing ground or air if the insulation does not remain dry.
in the cavity in less than one hour. Insulations will be
With reference to FIGURES 1, 2, 11 and 13, the evap
characterized as being of intermediate resistance if it
oration channel which is a principal feature of my inven
requires a day to a week for any appreciable amount of
tion is identi?ed by the reference character 22, and is
water to accumulate in the cavity 31. High resistance
shown located within the insulation 25, between the heat
insulation is characterized by the ‘fact that no appreciable
ed ?uid conducting pipe 23 and the outer boundary of
moisture accumulates in the cavity 31 even after two
the insulation 24. Other examples are identi?ed and dis
Weeks under test. It should be pointed out that even with
cussed in connection with other ?gures.
The present invention corrects the di?iculties cause
high resistance insulation, the surface of the cavity will
be sensibly damp because no evaporation takes place
by accidental ?ooding of the insulation by permitting the
from the surface of the cavity because the air in the
insulation to be drained by the drain cocks 20 and 21 of
FIGURE 1. The drain cocks 20 and 21 in actual prac
tice might be replaced by any type of trap or sump with
automatic pump depending on the type of service.
closed vessel 33 and in the cavity 31 has a relative humid
ity at or near 100% saturation.
Although engineers would intuitively place at least one
vapor permeability so that any location in a body of in
sulation can gradually dry if a means is provided for
removing water vapor more rapidly than water enters
of the channels such as 22in the lower part of the insula
Even though insulation has high resistance to the mi
gration of liquid water, it usually has sufficient water
tion, I have found that satisfactory ?ood drainage takes
place for any location within the insulation, because in 75 as liquid or vapor.
The moisture level in the insulation is also a function of
the temperature. If the heated ?uid conducting pipe 23 has
if the channel 22 were at a cooler location in the outer
a temperature above the toiling. point ‘of water at at
The most desirable location within the insulation for
mospheric pressure, then the insulation between the Sur
the evaporation channel 22 can be determined on the
face of the pipe 23 and the place in the insulation where Ul basis of the following considerations.
the temperature is equal to that of boiling water will be
If the insulation has high resistance to the migration
essentially oven dry. Any free moisture in this zone of
of water, then channel 22 can be placed far out in the
the insulation will be driven by the thermal gradient to
outer zone where the temperature will be a minimum.
the place where the temperature is below the boiling
This location reduces thermal losses by the air currents
point of water.
?owing through the channel.
The temperature gradient for a four inch diameter pipe
If the resistance to migration of water is intermediate,
operating at 350° F. surrounded by six inches of in
then the channel 22 must be placed near the 210° F.
sulation of the con?guration shown in FIGURE 2 is
zone to achieve maximum temperature for the conse_
given in FIGURE 7 which is a plot of temperature in
quent more rapid evaporation. With insulation of low
degrees F. vs. distance from the pipe surface in inches. 15 water migration resistance, it will not be possible to evap
The temperature gradient for a similar eight inch diam
orate water as fast as it can run into 22. In this case
eter pipe operating at 750° F. and surrounded by twelve
channel 2?..would merely serve as a drain through the
inches of insulation is given in FIGURE 8.
drain cocks 20‘ and 21, unless a casing is used to keep out
In the preferred forms of the present invention, the
the bulk of the water, in which case my invention can
channel or vent passage 22 is located at ‘a point inter 20 function with low resistance insulation.
mediate the outside surface of the insulation and the
The migration of water through the insulating con
point within the insulation where the temperature is at
crete constituting an underground heating distribution
the temperature of boiling water. This region has ‘been
conduit can be viewed analogously to the ?ow of elec
referred to as the outer zone in the succeeding discus
tricity through a shaped conductor.
sion, and the inner zone referred to subsequently extends
The resistance of the insulating concrete to the migra
from the ‘outer surface of the pipe 23 to the aforemen
tion of the water is equivalent to the electric or ohmic re
tioned point in the insulation where the temperature is
sistance. The system can be considered to be a balanced
Within the outer zone as defined
circuit in which the water entering and passing through
above, the preferred location for the vent passage for
the solid portion of the concrete is equal to the vapor
steam carrying systems will normally ‘be in the range 30 evaporation. The water movement from the external
from 0.3 to 0.9 times the distance from the outermost
surface to the air space, is dependent in part on the total
pipe surface to the outermost boundary of the insula
resistance. If the resistivity of the solid part of the sys
tem is relatively high, a tolerable flow of water can be
More speci?callyrwith steam carrying pipes operating
obtained without casings or with a relatively low resist
that of boiling water.
at quite high temperatures (as exempli?ed in FIGURE
ance coating or casing. For example, a wash of Port
8) a convenient location for the channel 22 is at the
land cement ‘base waterproo?ng paint can be used as a
area where the temperature is about 210° F. ‘For lower
casing. Numerous varieties of such waterproo?ng paint
‘are commercially available as cement paint to waterproof
temperature work, it may be located ‘at an area having
a temperature of about 170° F.
cement blocks and basement walls. If desired, an addi
In the insulated pipe system for which the temperature 40 tional layer of water resistance can be added by applying
gradient is given in FIGURE 7, the inner zone is approxi
over cement paint a bituminous mopping. Sufficient re
mately the ?rst two inches going ‘out from the pipe.
sistance can also be obtained with the bituminous coating
The outer zone is from this two inch position out to
alone, i.e., a water emulsion type asphalt coating can be
the surface of the six inch thick insulation. In the ex
placed on the outer surface of the insulation.
ample of FIGURE 8 the inner zone is approximately the
If the air current circulation through the duct is small,
?rst seven inches out from the surface of the pipe. The 45 then the total resistivity must be relatively large. How
outer zone is from seven inches ‘out to the surface of the
ever, if a reasonable quantity of moisture is evaporated,
twelve inch thick insulation. The exact location of the
then a lower resistance can be tolerated and it is possible
210° F. zone in any given system ‘will be a function of
to get along with the resistance of only the solid part of
the insulating concrete.
the moisture content of the system. More precisely the
210° F. zone is de?ned as the 210° F. isothermal sur 50
FIGURE 3 shows the cross section of a speci?c example
face within the insulation and its shape depends on the
of my invention which was built to obtain the thermal
exterior shape of the insulation and the size and con?gu
efficiency data shown in FIGURE 9. Insulating con
rations of the heated pipes. This isothermal is illus
crete of high water migration resistance was poured
trated in FIGURES 13 and 14 by the dotted line 47.
around a four inch pipe coated with a parting agent to
As the insulation dries out the 210° F. zone moves out 55 prevent adhesion of the concrete to the steel pipe. Two
ward and becomes narrower. The width of the 210° F.
evaporation channels 35 are located in the outer part of
zone is illustrated in FIGURES 7 and 8 by the essentially
the defined outer zone.
horizontal part of the curve at approximately 210° F.
High water migration resistance insulating concrete
At ?nal dryness it will be quite narrow and occupy a
was made with the following ingredients:
position proportionally located between the temperature 60
of the pipe 23 and the temperature of the outer surface
Portland cement
of the insulation. As an average for 350° F. heated
?uid systems the inner zone or above 210° F. zone oc
Expanded vermiculite (small particle size,
94 lbs.
waterproofed by method of Sucetti Patent
cupies approximately the ?rst one-third to one-half of
the distance out from the surface of the pipe 23. The
Emulsi?ed asphalt ______________________ _. 3 gallons
outer zone constitutes the remaining distance out.
Water ________________________________ _. 21 gallons
The moisture content of the insulation in the inner
zone is negligible because any free moisture present
would boil off or migrate to the cooler outer zone of the
insulation where it condenses.
Thus the channel 22 when located in the inner zone re
ceives only the limited amounts of water that can diffuse
from the outer zone back into the channel 22. Also the
temperature losses due to circulating air are larger than 75
No. 2,355,966) ____________ __' ________ __ 6 cu. ft.
The wet density of this mix was 60‘ lbs./ cu. ft.
A layer of
insulating concrete was poured approximately three
inches deep or up to the level of the line C-C in FIG—
URE 3. A U shaped metal strip was pressed into the
concrete to form U shaped grooves 37 of FIGURE 3.
The shaped channel was located so that approximately
one inch of insulation was present on the outside of the
After the concrete hardened the U shaped metal chan
was ?ooded with water.
nel in the concrete, thus forming an approximate oval
with the surface of the lower half of the oval being con
crete and the upper half metal.
The rest of the insulation shown in FIGURE 3 was
It should be pointed out that
this system hasno casing. Air continued to circulate
through channels 35 thus removing water by evapora
nel was removed and inverted over the U shaped chan
The system was left in the ?ooded condition for
seven days.
During this time no change in the heat loss
was observed, indicating that the circulating air current
poured leaving the metal inverted U forms in place. The
was able to carry away water vapor at the same rate
exact shape of the oval is of no importance to my in
that liquid water was entering the insulation,
At the end of the seven day ?ooding period the water
FIGURE 4 shows a few convenient shapes 33, 39, 4t} 10 was removed and the system continued in normal opera
tion for ten more days. At this period the heat loss was
down to 205 B.t.u. The system was again ?ooded for ten
days and the heat loss remained steady at 205 B.t.u. At
the end of this ten day ?ooding the water was removed
and 41 of channels that can be of any convenient con
struction material. If the material is permeable to water
it increases the evaporation area. With any of the shapes
illustrated in FIGURES 2, 3 and 4, it is desirable that
the channels have a cross sectional area of less thn 15%
of the cross sectional area of the insulating concrete, and
and normal operation continued.
With thirty days of additional normal operation the
preferably less than 10% of that ?gure.
heat loss reached an equilibrium value of the heat loss at
148 B.t.u. The system was again ?ooded and no ap
With appropriate choice of metals in regard to the
electro chemical series for metals and proper electrical
connection between the pipes and the forms these in
preciable change in efficiency was observed. These data
verted forms can serve the supplementary function of
as a function of days of operation. The flooding periods
providing electrolytic corrosion protection for the pipes
are evident as the horizontal part of the curve.
contained within the insulation. To this end, the metal
of the channel should be electronegative with respect to
the metal of the heat conducting pipe. The ends of the
channels 37 and 38 communicated to the atmosphere
with stand pipes, one pipe preferably longer than the
other to aid syphon action circulation of air.
Another embodiment of my invention is shown in FIG
URE 12 in which four heated pipes are contained in a
are presented in FIGURE 9 where heat losses are plotted
single unit of insulation. Two evaporative channels 45
and 46 are employed to carry off the water vapor.
Still another embodiment of my invention is shown in
FIGURE 13, where a single heated pipe 23 system is
shown equipped with a single evaporative channel 22
placed in the top section of the insulation. The insula
tion in this system is given protection in the form of 21
Portland cement paint ‘outer casing 48. The bottom of
There are many additional ways in which experienced
construction workers can introduce the channels. Of
these possible ways, the following serve as illustrations:
(1) the channels might be formed by tubes made of
stiff water permeable materials such as cardboard, ?ber,
plasters, screening, ceramics or perforated metal. The
tubes are fastened at the appropriate place in the form
used to hold the insulation during the time required for
setting. The joints between tubes are taped to exclude
the wet concrete and the tubes are left in place.
(2) In the production of preformed factory-made sec
tional insulation, the channel can be formed by a man
drel in the mold so arranged that it can be removed after
the insulation takes shape. FIGURE 11 shows a cross
section of one example of such a preformed section.
Naturally it is necessary to cement the ends of the sec
tions together to avoid the possibility of excessive move
ment of water into the insulation along the radial joints
between the sections.
The preformed factory made sections can be made
solid as shown in FIGURE 11, in which case they are
slipped on endwise over the end of the heated ?uid con
ducting pipe or the sections can be split longitudinally in
the manner that is conventional for preformed rigid sec
channel 45 or 46 or both can serve as the drain channel.
this system consists of a structural concrete base pad or
In this case an insulating concrete of inter
mediate resistance to water migration can be used be
cause the cement paint limits the in?ltration of water.
I foundation.
Cement paint is a typical example of a semipermeable
casing. Bituminous coatings could be applied instead of
the cement paint or on top of the cement paint.
In general, a small leak in an otherwise completely im
permeable casing will cause the system to operate the
same as with a semipermeable casing.
The water enter
ing the casing through a small hole will distribute itself
by capillary action between the casing and the insulation.
It is usually not convenient or practical to achieve a non
capillary bond between the insulation and the casing.
In FIGURES 13 and 14 typical ?ow lines for water in
?ltrating from the outside are shown. FIGURE 15
shows the less frequent, but important case of the ?ow
lines from a break in the heated ?uid pipe. FIGURE 15
also shows my invention applied to a system having an
tional insulation. In this case channel 22 can be con
tained entirely within one of the sections or it can be
impervious casing 49.
placed in the ‘longitudinal boundary between the sections
factory-made section of insulation in which the evapora
tive channel has been enlarged to the place where it is a
concentric ring within the body of the insulation. In this
form, it is desirable that the air space 22 constitute about
so that one side of the channel is formed by one half of
the sectioned insulation and the other side of the channel
is formed by the other half of the sectional insulation.
The effectiveness of my invention can be demonstrated
through heat loss measurements with the system illus
trated by FIGURE 3.
FIGURE 9 shows the measured heat loss as a function
of time.
FIGURE 5 shows the cross section of a preformed or
5 to 50% of the space between the outer surface of the
pipe 23 and the outermost periphery of the insulation,
and that the outer cylinder of insulation, extending from
the outer peripheral boundary of the air space to the
outermost periphery of the insulation constitute about 30
to 95% of said space.
Initially, poured in place insulating concrete has a
large moisture content which results in a relatively poor 65 FIGURE 6 shows another possible con?guration which
initial thermal e?’iciency. A four inch diameter pipe op
is possible with either job formed or factory formed
erating at 350° F. is considered e?cient when the heat
insulation. The ‘factory formed section illustrated in
FIGURE 11 is particularly simple and easy to fabricate.
losses are about 200 B.t.u. per hour per lineal foot of
It is also easy to cement together the ends of the sec
After the completion of an initial warm up period, the 70 tions to achieve water tight joints.
FIGURE 3 example showed a heat loss of 364 B.t.u. per
While there are above disclosed but a limited number
lineal foot per hour. Continued operation with normal
of embodiments of the structure, process and product of
thermal syphon circulation of air through channels 35
the invention herein presented, it is possible to produce
resulted in a lowering of the heat loss so that at six days
still other embodiments without departing from the in
the loss was 241 B.t.u. At this time the whole system 75 ventive concept herein disclosed, and it is desired there
fore that only such limitations be imposed on the ap
pended claims as are stated therein, or required by the
prior art.
The invention claimed is:
5. In a heat distribution system comprising ‘an im
pervious pipe arranged tocarry a heated ?uid and a
monolithic jacket of lightweight, moisture vapor per
meable insulating material thermally insulating said pipe
1. ‘In a heat distribution system comprising an im
about its entire periphery from a colder surrounding en
pervious pipe arranged to carry a heated ?uid having a
temperature in excess of the boiling point of water and a
monolithic jacket of lightweight, moisture vapor perme
vironment having a temperature less than the boiling
point of water at the prevailing atmospheric pressure, said
insulating material having at least one longitudinally ex
tending vent passage formed in said insulating material
about its entire periphery from a colder surrounding en 10 in spaced relation to said pipe, said vent being in com
vironment having a temperature less than the boiling
munication with free air, the improvement comprising
point of water at the prevailing ‘atmospheric pressure,
providing said vent passage in the region of insulation
said insulating material having at least one longitudinally
where the temperature of the insulation is intermediate
extending vent passage-formed in said insulating material
the temperature at the outside surface of the insulation
in spaced relation to said pipe, said vent being in com
and the temperature inside said pipe, and in which said
able insulating material thermally insulating said pipe
munication with free air, the improvement comprising
vent passage has a cross-sectional area of less than about
providing said vent passage in the region of insulation
15% of the cross-sectional area of said jacket.
Where the temperature of the insulation is intermediate
the temperature or said environment and the temperature
References Cited in the ?le of this patent
of boiling water.
2. The system of claim 1 in which the center of said
vent passage is located at a distance in the range from
0.3 to ‘0.9 times the radial dimension of the jacket meas
ured from the outermost pipe surface to the outermost
Meehan ____________ __ June 19, 1888
Gottwald ___________ __ Feb. 27, 1931
Gysling ____ __. ______ __ May 25, 1937
God _______________ __ Aug. 15, 1944
3. The system of claim 1 in which the center of said
vent passage is located at a point Where the temperature
of the insulation is about 210° F.
4. The system of claim 1 in which the center of said
vent passage is located at a point where the temperature 30
of the insulation is about 170° F.
McLeish ___________ __ Oct. 10, 1944
Rohrman ____________ __ Aug. 7, 1956
O’Rourke et a1. ______ .._. Jan. 21, 1958
Broadway et a1. _______ __ July 28, 1959
periphery of said jacket.
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